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Jason, Service Technician
Category: Electrical
Satisfied Customers: 4278
Experience:  Over 20 years of experience in all types of installations, troubleshooting, and repairs.
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Can I connect 4 prong 220V 30 amp to a 3 prong 220V 30 amp

Customer Question

I have a shed disconnected from main power, no power at all, but is wired. I want to use my portable generator to light it up when out there using tools. I want to go into the 220 volt 3 prong wired outlet from the 4 prong 220 genset, it is possible and safe.
Submitted: 8 years ago.
Category: Electrical
Expert:  Jason replied 8 years ago.
HiCustomer Let me make sure I understand you. Do you have a 3 prong outlet in the shed now? If so, where do the wires connected to it go, or come from? In other words, where is the other end of the wires connected to the 3 prong outlet?
Customer: replied 8 years ago.
red and black to breaker 30 amp
white neutral
Expert:  Jason replied 8 years ago.

Okay, good information. Do you have a small subpanel in the shed with no main wires coming from the house to feed it?

Customer: replied 8 years ago.
Correct, the power to the shed is dissconnected completely, I use it because it has a roof and concrete floor for projects. It has lights, 4 outlets, no gfi's and the old 220 3 prong outlet.
Expert:  Jason replied 8 years ago.

Thank you for asking your question on Just Answer!!!

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Okay. Thanks for your patience with my questions. The information you have given me is very helpful. What I would recommend in your case is to connect the cord that will plug into the generator to the mains in the shed panel. I would also recommend driving 2 ground rods outside the shed and connecting a grounding electrode conductor to the 2 rods and the ground/neutral bar in the shed panel. I would replace any standard outlets in the shed with GFI outlets. Since the generator will be considered a service and not a subpanel, you will connect ground wires and neutral wires to the same bar, instead of seperate bars like you would if the shed panel was fed by the main panel in the house. If any of this is unclear, please let me know. Also, if you need a diagram showing how to connect the system, let me know and I would be happy to post one for you.

Hope this helps you out. If you should need anything further please don't hesitate to ask. Have a great night!

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Customer: replied 8 years ago.
Reply to Jason's Post: I understand but would like a diagram, why connect ground and neutral to same bar? Just curious.
Expert:  Jason replied 8 years ago.

The reason the ground and neutral will connect to the same bar is because the generator is considered a service (or main panel) and the shed panel is your access to the branch circuits of that service. If the shed panel were fed from the house, it would be considered a subpanel, not a service. The grounding/bonding requirements for subpanels are different than they are for main panels. I am working on your diagram now, and I will get it posted as soon as it's done.

Jason and 2 other Electrical Specialists are ready to help you
Expert:  Jason replied 8 years ago.
Okay, here's your diagram. Sorry it's a little messy, I was trying to draw it quickly since you were waiting. Thank you for accepting my answer. Let me know if you need anything else. Best of luck to you with your wiring project.

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